Bending/shaping machines or also stirrup-making machines are known, hereafter bending machines, in which bending units or devices are fed with long metal products, such as metal products from a roll, or pre-cut bars, in order to make reinforcement stirrups for the building trade. Hereafter these base materials, whether from a roll or already in bars, will be referred to generically as metal products.
By metal products we mean therefore a nominally round product obtained by hot or cold rolling, with a diameter that normally varies from 5 mm to 20 mm and provided, or not, with ribs that are useful in the case of reinforcements for the building trade.
It is also known that upstream of the bending unit, bending machines have a drawing unit to feed the metal product to the operating units of the machine, such as at least a shears and at least a bending unit.
Normally, apart from the drawing unit, a straightening unit is provided and a unit, possibly structured in the straightening unit, suitable to eliminate torsion in the metal product.
Furthermore, when two or more metal products are fed, the drawing unit has a drawing motion to be able to feed the same lengths simultaneously.
It is known, in fact, that the metal product is not always already linearized before it is fed to the bending unit.
It is also known that the metal product has a tendency to rotate around its axis when the internal tensions are released, for any reason whatsoever.
It is also a known problem that during the drawing function, due to the forces in play needed to have a controlled drawing, in order to grip the metal product correctly and draw it, the ribs present on the periphery are often deformed, making the metal product at least partly lose its effect of adhering to a cast of concrete.
It is also a known problem that, when two or more metal products are drawn simultaneously, it is unlikely that the drawing effect will translate the same length in the two or more metal products, due to the differences in size which occur at different points in the metal products drawn.
It is therefore obvious that a bending operation performed on the metal product is conditioned by the deficiencies in said product, so that the geometric shapes eventually made with the metal product not only do not maintain the desired geometric disposition, but moreover they do not even maintain the flat spatial disposition.
In these cases, the stirrups deriving from such bending are low quality and unreliable once installed, and therefore they are normally discarded, or they require longer installation times. To this must be added the fact that, in the case of metal products for reinforcement rods, given the continuous variation in their section, the correct and accurate straightening and/or drawing become uncertain, inconstant and not uniform.
It must be indicated here that metal products for reinforcements have an extensive range of nominal diameters that can go from 5 mm to 20 mm and more, and that a bending machine must always be able to work at least most of this range of measurements and obtain in any case a perfect product.
It is also known that the level of problems posed by a small metal product is different from the problems posed by a metal product with a bigger diameter.
It must also be noted that, in a bending machine, the drawing unit assumes another considerable importance, since it is also responsible for defining the measurements required on each occasion between one bending operation and the next.
This becomes even more important when the drawing unit works two or more metal products simultaneously.
When the drawing unit does not obtain its purpose constantly and without mistakes, it is not possible either to obtain stirrups or other shapes of metal product having the desired sizes and shapes, or to obtain, in sequence or otherwise, a plurality of identical stirrups or other shapes.
One purpose of the present invention is to obtain a drawing unit that does not damage the metal product being worked.
Another purpose of the present invention is to obtain a drawing unit that can operate continuously and precisely with any type of metal product, in particular metal products for reinforcements.
Another purpose of the present invention is that the drawing unit feeds precisely both one metal product and two or more metal products simultaneously.
Another purpose is that the drawing unit also performs the function of straightening.
Another purpose of the invention is that the drawing unit prevents the metal product from rotating on itself.
The Applicant has devised, tested and embodied the present invention to overcome the shortcomings of the state of the art and to obtain these and other purposes and advantages.